1. Field of the Invention
The present invention relates to a system that monitors a plurality of sensors to detect when any one of them senses a fault condition, and more particularly to safety monitoring equipment for a cable vehicle system, such as an aerial tramway or a chair type ski lift.
2. Description of the Related Art
Elevated transport systems such as an aerial tramway, cable car, or a chair lift, has a vehicle attached to a continuous loop of cable that extends up a mountain and then returns back down the mountain. A series of towers have pulleys, also called sheaves, on one side over which the cable rides in the upward direction and another set of pulleys on the opposite of the tower over which the cable rides on the downward direction. An electric motor or fuel powered engine is typically located at the bottom of the mountain to drive the cable around the circuit formed by the tower assembly and thereby up and down the mountain.
The major safety concern is that the cable properly rides over the pulleys. The most fundamental safety system for monitoring the cable is an electrical conductor that forms a wide loop through which the cable passes upon traversing past a tower. Normally the cable does not contact this conductor and electricity flows through the conductor providing an indication of the satisfactory operation of the cable. If the cable jumps off a pulley, the cable saws through the electrical conductor, interrupting the flow of electricity thereby providing a signal to a monitoring device that a cable malfunction occurred. This type of rudimentary sensor provided only an indication after a catastrophic failure took place. It became desirable to detect a potential malfunction before a catastrophic failure occurred.
As a result, an apparatus was devised that sensed the position of the cable on the pulleys to detect if the cable wandered to one side or came off a pulley. That sensing apparatus detected when the cable came out of a center groove in the pulley, upon which case, the cable vehicle system was shut down before the cable became fully dislodged. A small deviation of the cable from the nominal location caused a reduction in the cable speed. If the deviation became greater, exceeding a given amount, the safety system shut down the elevated cable system.
Relatively sophisticated proximity sensors have been developed to detect the relative location of a metal object with respect to the body of the sensor. These sensors also have internal diagnostic capability which provides information to a central monitoring system when the sensor becomes unreliable or inoperable. Such sophisticated proximity sensors are marketed under the iProx™ brand name by Eaton Corporation of Cleveland, Ohio, USA.
On an elevated cable vehicle system, it may be relatively difficult and time consuming to travel to the tower on which the inoperable cable sensor is located in order to perform maintenance activity. As a consequence, it often is desirable to be able to continue operating the cable vehicle system until a malfunctioning sensor can be repaired or replaced. However, previous safety systems disabled the operation of the entire cable vehicle system even when only one sensor was inoperative. The only solution was to disable the entire safety apparatus and operate the cable system without cable monitoring.
Therefore, it is desirable be able to bypass a malfunctioning sensor and continue otherwise normal operation of the safety monitoring system. It also is important to be able to locate the particular tower and even the specific sensor that has malfunctioned, in order to expedite maintenance and repair.